1. Field of the Invention
The present invention is directed to apparatuses, methods and computer programs for actuating a disconnect clutch such as can be used particularly for vehicles with hybrid drives and which is arranged between a first drive unit and a second drive unit of a hybrid drive.
2. Description of the Related Art
By hybrid drive is meant a vehicle drive having more than one drive unit or drive source. In this case, a first drive unit is generally an internal combustion engine, e.g., an Otto engine or diesel engine, while a second drive unit is generally designed as an electric machine or electric motor. Based on a variety of factors, hybrid drives can be classified as micro hybrid drives, mild hybrid drives, medium hybrid drives or full hybrid drives. A full hybrid drive allows driving with the electric motor as exclusive drive source. Although the following description addresses full hybrid drives in particular, embodiment examples of the present invention are not limited exclusively to full hybrid drives.
A distinction can be drawn between a serial hybrid system and a parallel hybrid system based on the arrangement and mechanical connection of the two drive units. In a serial hybrid system, the entire output of the internal combustion engine is converted into electrical energy by a generator so that the vehicle is driven exclusively by the electric motor powered by the generator. However, present-day passenger cars with full hybrid drive use what is known as a parallel hybrid system. In this case, the internal combustion engine and the electric motor both drive the axle drive and wheels. The electric motor draws its electric power from a battery which is charged by the electric motor or the electric machine itself in that the latter is operated as a generator during driving.
FIG. 1 is a schematic diagram showing the construction of a conventional powertrain 100 of a full hybrid vehicle.
The parallel hybrid drive 100, shown schematically, has a serial arrangement of an internal combustion engine 110, an electric machine 12 constructed as an engine starter generator, and a drive transmission 130 connected to the driven side of an axle drive. Arranged between the internal combustion engine 110 and the electric machine 120 is a disconnect clutch (K0) 115 which allows the internal combustion engine 110 to be disconnected from the rest of the powertrain and accordingly makes it possible to change to a fully electric drive operation. The powertrain 100 further comprises a starting clutch 125 which is coupled between the electric motor 120 and a transmission input shaft 126 of the transmission 130. Accordingly, the starting clutch 125 can couple a shaft 121 of the electric motor 120 to the transmission input shaft 126 so that the transmission input shaft 126 is indirectly coupled to the electric motor 120 by the starting clutch 125. Here, the term “couple” is to be understood as a torque-transmitting coupling between the electric motor 120 and transmission input shaft 126.
The disconnect clutch (K0) 115 is driven by the internal combustion engine 110 via a clutch input shaft 111. On the output side, the disconnect clutch 115 is connected to the electric machine shaft 121. The internal combustion engine 110 can be started by a separate belt starter or a conventional starter. But the internal combustion engine 110 can also be accelerated by closing or applying the disconnect clutch (K0) 115. In either case, the disconnect clutch 115 can be fully closed at the latest when the internal combustion engine 110 has reached the electric machine speed. After this point, the internal combustion engine 110 is fixedly coupled to the rest of the powertrain and can accordingly inject its torque for the propulsion of the vehicle.
Various possibilities for actuating the disconnect clutch 115 are known from the prior art. For one, the disconnect clutch 115 can be actuated, for example, via a release lever, in which case an electromechanically or hydraulically actuated plunger can exert a force on the release lever. A conceivable alternative is to actuate the disconnect clutch 115 via an integrated electromagnetic actuator. However, an actuator of this kind will not be further considered within the framework of the present invention. Further, it is known to actuate the disconnect clutch 115 by means of a concentric slave cylinder (CSC) or central release mechanism; in this case, an actuating force for actuating the disconnect clutch 115 is generated by creating hydraulic pressure in the concentric slave cylinder. A concentric slave cylinder combines release mechanism and slave cylinder in one unit. The concentric slave cylinder offers clear advantages over conventional mechanical-hydraulic systems with respect to design, construction, upkeep and operation.
For purposes of integrating the electric machine 120 in present-day powertrains, an actuating system for the disconnect clutch 115 should be very compact and arranged ideally radially inside the electric machine 120. In view of these prerequisites, solutions using the release lever appear less attractive; therefore, embodiment examples of the present invention are concerned with actuation of the disconnect clutch 115 by means of a concentric slave cylinder.
To generate an actuating pressure for the disconnect clutch 115, which can be in the range of about 40 bar for compact actuating systems, it is known to use external hydraulic drive units. These external hydraulic drive units comprise a master cylinder which is generally actuated by an additional electric motor provided in addition to the electric machine 120. Control electronics are additionally required for this purpose. Actuators of this kind are also found in various automatic shifting transmissions. However, these known solutions for generating the actuating pressure for the disconnect clutch 115 entail high costs, greatly increased weight and a large installation space.